There are methods known in the related art adopted to acquire a noise-free image by transforming an original image to reversible multiple-resolution images and reconstructing the image through adjustment of the transformation coefficients. A typical example of such a method is disclosed in patent reference 1. Patent reference 1 discloses a method for acquiring a noise-free image by spatially filtering for noise removal, the high-frequency subband coefficients in the multiple-resolution images resulting from the transformation and then inverse-transforming the image. Patent reference 2 discloses a contrasting method through which noise is sequentially removed from reduced images on the low-frequency subband side, which are generated on a temporary basis during the process of the multiple resolution transformation.
Patent reference 3 discloses a method through which, instead of removing noise directly on the transformation coefficient planes of the multiple-resolution images resulting from the transformation as described above, noise is removed by extracting noise components contained in the high-frequency subband transformation coefficients corresponding to LH, HL and HH resulting from the multiple resolution transformation via orthogonal wavelets, combining only the noise components through inverse wavelet transformation and subtracting the synthesized noise component from the original image, so as to assure better ease in the handling of the noise components. This method allows the extent of noise removal to be adjusted easily by applying a constant multiple factor dependent upon the image structure in the real space to the synthesized noise component prior to the final subtraction processing.
Patent reference 3 also presents an application example in which a similar technology is adopted in edge emphasis, whereby edge components, as well as the noise components, are extracted from the subband coefficients resulting from the multiple resolution transformation, the extracted edge components are combined, a constant multiple factor dependent upon the image structure is applied to the synthesized edge component in the real spatial plane and then the product is added to the original image.
Patent reference 1: U.S. Pat. No. 5,526,446
Patent reference 2: U.S. Pat. No. 6,937,772
Patent reference 3: U.S. Pat. No. 6,754,398